Preparation of amino-phenols and primary aryl amines conjointly



Patented Oct. 18, ,1932

UNITED "STATES PATENT OFFICE EDGAR C. BRITTON AND RAY I). HOLMES, OF IVIIDLAN D, M'IOHIGAN, ASSIGNORS TO THE DOW CHEMICAL COMPANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN PREPARATION 0F AMINO-PHENOLS AND PRIMARY ARYL AMINES CONJ'OIN'ILY No Drawing.

The present invention relates to the preparation of amino-phenols by the reduction of the corresponding hydroxy-azo compounds, and in particular to methods wherein such reduction is effected through the agencyof hydrogen sulphide or an alkaline sulphide in the presence of Water.

It is known that oxy-azobenzol may be reduced to para-amino-phenol and aniline in a strongly alkaline-medium by heating a mixture of such oxy-azobenzol, sodium sulphide and sodium hydroxide to 180 (1, with the addition of a limited amlougt of water jusp sufficient to su l the 1 rogen requirec pp y (D. R. P. 95,755). Jacobson and Henigsberger (Ber. 36; 4-110) carried out this reduction at a lower temperature by the use of ammonium sulphydrate or sulphide in an alcoholic medium, obtaining thereby a yield of to per cent para-amino-phenol. More recently it has been proposed (Brit. Pat. 179,758) to conduct the reaction in an aqueous medium consisting of a solution of so- 1 dium carbonate in which the oxy-azobenzol is dissolved or suspended bypassing hydrogen sulphide or a gas containing hydrogen sulphide through the mixture at a temperature of about 100 C. q

We have found that none of the aforementioned methods lead to a commercially satisfactory conversion of raw materials into the desired products. The yield of amino-phenol particularly, as obtained by 1 such methods, falls far short of the theoretical for the materials actually reacted, and almost invariably the product is badly discolored and contaminated with impurities diflicult of removal. For instance, when it is attempted to effect the reduction by passing hydrogen sulphide gas into the hot aqueous mixture, the absorption of gas is found to be quite incomplete,considerable volumes thereof escaping from the reaction vessel,

' thus necessitating the provision of suitable,

means for their recovery which adds appreciably to the cost of the product. We have now found that losses of hydrogen sulphide may be substantially avoided and a higher yield of a purer product may be realized if Application filed March is, 1929. Serial No. 348,356.

the reaction is carried out with active hydrogen sulphide formed in statu nascendi within the reaction mixture. In other words, by such procedure afar more complete ab sorption of the gas is attained and side reactions leading to the formation of decomposition products are largely prevented.

\ To the accomplishment of the foregoing and related ends, the invention, then, consists of the steps hereinafter fully described and particularly pointed out in the claims, the following description setting forth certain procedure illustrating a few of the ways a in which the principle of the invention may be used. p

The generation of hydrogen sulphide within the reaction mixture may be conveniently accomplished by the action of an acid upon a sulphide, preferably a water soluble sulphide, e. g., asulphide of an alkali or alkaline earth metal. An advantage incident to the use of an alkali or alkaline earth metal sulphide is that the aqueous solution thereof has a pronounced alkaline reaction, sufliciently so that the hydroxyazo compound may be completely dissolved therein at ordinary temperatures. On the other' hand sodium carbonate, for instance, .has only a limited dissolving power for hydroxy-azo benzeneor allied compound, particularly at ordinary temperatures, so that such compound remains largely in suspension rather than in solution when the reaction is carried out in an aqueous sodium carbonate solution. By choosing an aqueous medium wherein the reactants are completely dissolved, and generating hydrogen sulphide in situ within the solution, we are enabled to secure substantially complete reaction and to avoid any material losses ofhydrogen sulphide.

While a. strong mineral acid, such as hydrochloric acid, may be used to react upon the alkaline sulphide for generating hydrogen sulphide, the rate of reaction therewith and, consequently, of evolution of gas may be excessively great unless such acid is slowly as a dilutesolution thereof.- It is often preferable to employa weaker acid, such as carbon dioxide, or anacidic salt, such as amadded quite I hydroXy-azo compound monium chloride, whereby a more effective control of the reaction may be exercised. If a sulphydrate, instead of a sulphide, be employed, such sulphydrate is itself of a sufliciently acidic character to bring about the reaction without the addition of another acid. Still another method of generating hydrogen sulphide consists in reacting between an aqueous caustic alkali solution and sulphur, this reaction taking place above 100 C. and preferably under pressure. In fact, the reduction may be brought about simply by heating an aqueous mixture containing the sulphide dissolved therein, the prolonged action of water upon the sulphide in the presence of the reducible hydroXy-azo compound suflicing to effectthe reaction. The time required, however, is much greater than when an acid is employed, and in general the latter procedure is preferred.

The various equations to show the relative quantities of materials involved in the reactions just referred to may be expressed as the following, wherein R and R represent aryl radicals which may be further substituted in the nucleus. Each molecule of hydroXy-azo compound is reduced to a mole cule of primary amine and a molecule of amino-phenol. Equation (1) represents the reaction when water alone is employed to react with the inorganic sulphide, the latter being converted to thio-sulphate;

With a monovalent acid, e. g., HCl, the reaction proceeds as in Equation (2) When CO is employed, the reaction takes place similarly, as in Equation (3) Then, in the case where hydrogen sulphide is formed by heating sulphur and aqueous caustic alkali solution, the reaction is expressed by Equation (5) For each mole of the hydroXy-azo compounds equivalents of hydrogen are required to effect the reduction. least, such hydrogen is supplied in the presence of a reducible substance by hydrogen sulphide, H 8, generated within the mixture and an alkali metal Theoretically, at

during reaction and acting as the reducing agent. This is most readily accomplished by the reaction of the acid employed with the metallic sulphide, viz;

However, other reactions also come into play for releasing H 5. For example, the hydroXy-azo compound is itself an acidic compound, which reacts With a basic sulphide, e. g., Na S, to form the corresponding sulphydrate or hydrogen, sulphide, viz;

(7) RN NROH-l-Na Sa RN:N.RONa+NaSH Finally the alkaline sulphide or sulphydrate, in the presence of an oxidizing, i. e., a reducible, substance, may be hydrolyzed by water, as in Equations (9) and (10) As will be seen from Equations (2), and (a), less acid or acid salt is employed than would be required to react with all of the alkali sulphide to liberate H 3 therefrom. This is done intentionally so that the reaction mixture will remain alkaline, and thereby hold in solution the sulphur formed in the reaction, probably as a polysulphide. Otherwise, if the solution becomes neutral or acid, sulphur is precipitated, in such case involvingja troublesome separation thereof before the principal reaction products are recoverablein pure form from the mixture. The conversion of the remainder of the alkaline sulphide in the mixture to active hydrogen sulphide is accomplished in accordance with one or more of Equations (7) to (10), inclusive. Accordingly, the principal reaction, as expressed by Equations (2), or l), is conducted throughout in an alkaline medium, the acid compound being added gradually and with vigorous agitation so that no excess of acid shall be introduced,

even locally, at any time. hen proceeding in accordance-with Equation (5), of course, such precautions are unnecessary. In either case, however, under proper control the hy drogen sulphide is absorbed as rapidly as it is formed, the utilization thereof being substantially quantitative.

The resulting reaction product consists of an aqueous alkaline solution containing the amino-phenol and sulphur dissolved therein, whilethe primary amine product forms a separate oily layer. T he latter is conveniently removed by distilling with steam, either at atmespheric or under reduced pressure, or maybe extracted by means of a solvent, such as benzene or the like. Extraction may at times be advisable, in case the amino-phenol tively weak acid, such as CO or to employ an acidic salt, such as NH Cl,thereby avoiding precipitation of sulphur which occurs when a strong mineral acid isused, particularly if an access over thefexactfamount. of

i acid required for neutralization shouldbe fortuitously added. The crystals of a1nino-. phenol are filtered and washed with hydrogen sulphide water, being obtained without recrystallization in a highly pure form and remarkably free from discolo ration.- An alternative procedure is to acidify the solution, after separation of the primary amine,

with an excess of strong mineral acid, thereby precipitating sulphur and converting the amino-phenol to the salt of the acid employed, such salt remaining in solution. The mixture is then filtered to remove sulphur andv the filtrate evaporated to crystallize out the amino-phenol salt.

In the following illustrative examples, various specific applications of our improved method are described in detail, but itlwill be understood that theinvention is not limited thereto. p Example 1.One mole hydroxy-azo-benzene was added to an approximately 15 per cent aqueous [solution containing 2 moles sodium sulphide. .The mixture was heated to about 100 C. and then 1 mole carbon dioxide j was passed in, such introduction requiring about 1 hour. Thereaction mixture was steam distilled to remove aniline and the hot residual solution filtered. The filtrate was treated with NHiCl to precipitate para aminophenol, and the crystals filtered off and washed with H S water. Yield of aniline, 96 per cent, and of para-amino-phenol, 88.6 per cent.

Example 2.One mole of gortho-toluene- :azo-phenol was dissolved-in a 25per1cent. aqueous solution containing 2 molessodium sulphide. The solution was heated to about 100 (1, and 2moles hydrochloricacid in 10 per cent. solution were added gradually during 1% hours. The mixture was then steam distilled to remove orthotoluidi ne and the residual solution filtered to clarify it. The filtrate was treated with ammonium chloride to precipitate the para-amino-phenol, the crystals of the latter. were filtered off and washed, with hydrogen sulphide water. Yield of ortho-toluidine, 100 per cent., and of paraTamino-phenol,65 per cent. 1 7

Example 3.One mole benzene-azo-3- -phenyl-4-phenol' was dissolved in a 20 per cent. aqueous solution containing 2 moles cent.

naphthol and moles sodium sulphide were dissolved to make an aqueous solution containing about 30 per cent. solids. The solution was heated to from to C. and maintained at such, temperature while 1 mole'carbon dioxide was passed in during approximately 1 hour. The hot solution was then filtered and extracted with benzene to separate the aniline therefrom. The aqueous layer was acidified with dilute sulphuric acid in excess and concentrated under reduced pressure. The hydrosulphate salt of 4-amino -l-naphthol crystallized fromthe solution on cooling and the crystals were filtered oil.

Yield of l-amino-l naphthol, 77 per cent.

- Example 5.'One mole hydroxy-azo-benzene was added to an approximately 24 per centfsolution of barium sulphydrate containing 1% moles of the latter. The mixture washeated to about 60? C. and the hydroxy azo-benzene was completely dissolved there'- by. The solution was then boiled for about 5 minutes without the addition of acid, to complete the reduction. Aniline was re moved by steam distillation, and the residual SOlIllL-ZOII was filtered and cooled to about 15 C. The para-amino-phenol was precipitated by adding a slight excess of ammonium chloride. A light colored product of very good quality was obtained. Yield of aniline, 94.5 per cent, and of para-amino-phenol, 62 per Example 6.-One mole hydr'oxy -azo-benzene was dissolved in 7 moles caustic soda in 15 per cent. aqueous solution, and an excess, about 8 moles, sulphur was added. The mix ture was placed in an ironautoclave provided with astirrerand heated vfor 5 hours at 125 C. Aniline was removed from the reaction product by'distilling with steam, and the residual solution was saturated with carbon dioxide to recipitate para-amino-phenol. Yield. of ani ine 96.5 per cent. and of paraamino-phenol 68per cent. l V

By similar procedure hydroxy-azo compounds generally, as .well as substituted derivatives thereof containing non-reducible substituent groups, may be treated for' the preparation conjointly of the corresponding salt as hereinbefore set forth;

jointlywhich comprises reducing the corresponding hydroxyeazo compound inan aqueousjsolutionby means of activ e.hydroge n sulphide generated in situ during such reaction.

2. The methodfor the preparation, of an aniino-phenoland' a primary arylamine conjointly which comprisesreducing the corresponding hydroXy-azo compoundin. an aque- Ous alkaline sulphide solution by means of active hydrogen sulphide generated in. ,situ during such reaction.

3. The method for the preparation of an amino-phenoland a primary arylamine conjointly which comprises reacting upon the corresponding hydroXy-a zo compound inan aqueous.alkaline'sulphide solution with an acidic compound.

4. The method. for ;the preparation of an amino-phenol and a primaryarylamine conjointlywhich comprises reacting upon thecorresponding hydroXy-azo compound man aqueous alkaline sulphide solution with an acidic compound in'amo'unt insufiicient ito neutralize completely such solution.

5. The meth'od for the preparation ofan amino-phenol and a primary arylamine con precipitated thereby.

jointly which,Icomprises reacting upon the corresponding hydroXy-azo compound in an aqueous alkaline sulphide solution with? an acidic compound in amount insufficient to neutralize completelysuch solution, removing such primary arylamine, acidifying the residual, aqueous solution and separating the amino-phenol precipitatedtherieby.

6. The method for thepreparation of an amino-phenoland aprimary arylamine conjointlyflwhich comprises reactin'glupon the corresponding hydroXy-azo compoundfin an aqueous alkaline sulphide solution with. an acidic compound in; amount 'insuflicient to neutralize completely such solution, removing such, primary arylamine by distilling with steam, acidifying the residual aqueous solution and separating the amino ph'enol 7. Themethod" for the .lprepara tion of para-amino-phenol I and aniline, 'conjointly which comprises reducing hydroXy-azo-benzenein an. aqueous mediumby means of. ac t1ve,hydr o.gen sulphide generated insitu duringsuchreaction.

. 8. The me h are; the preparation ofparaamiwphenol nd. time ei ieintlyr sh wav comprises reducing hydroxyazo-benzene in an aqueous alkaline sulphide solution by means of active hydrogen sulphide generated in situ during such reaction.

9, The method for the preparation of para-amino-phenol' and aniline conjointly which comprises reacting upon hydroxy-azobenzene in an aqueous alkaline sulphide solution with an acidic compound. 7

10. The method for the preparation of para-amino-phenol and aniline conjointly which comprises reacting upon hydroxyazo benzene in an aqueous alkaline sulphide solution with an acidic compound in amount insuflicient to neutralize completely such solution,

i 11.. The method for the preparation of para-amino-phenol and aniline conjointly which comprises reacting uponhydroxynzobenzene in an aqueous alkaline sulphide solution with an acidic compound in amount insuflicient to neutralize completely such solution, removing aniline by distilling with steam, acidifying theresidual aqueous solution and separating the amino-phenol precipitated thereby.

12. The method as set forth in claim 11, sodium sulphide being used for the alkaline sulphide therein.

13. The method as set forth in claim 11, carbon dioxide being used for the acidic compound therein.

14. The method for the preparation of an amino-phenol and a primary arylamine conjointly which comprises dissolving the corresponding hydroXy-azo compound in an aqueous alkaline sulphide solution, heating to a temperature between about and the atmospheric boiling point of the mixture while gradually adding an acidic compound in amount equivalent to about one-half that theoretically required to react with the sulphide present to convert the same completely to hydrogen sulphide, then separating the relatively insoluble primary arylamine from the aqueous solution, acidifying the residual solution and separating the amino-phenol precipitated 7 thereby.

15. The method for the preparation of para-amino-phenol and aniline conjointly which comprises dissolving hydroXy-azobenzene in, an approximately 15 per cent aqueous sodium sulphide solution in proportionof one mole of such hydroxy-azo compound to two moles of such sulphide, heatingtoapproXima-tely 100 C. while gradually addingabout vone mole of carbon dioxide; distilling with steam ,to remove aniline, acidifyingthe residual solution to a weak acid reaction, and filtering para-amino-phenol precipitatedthereby from i theaqueous solution.

Signed by us this 15 day of March, 1929.

- EDGAR C. BRITTON.

RAY D. V 

